The present inventive concept relates to an oscillation signal generator, and more particularly, to an oscillation signal generator for compensating for a phase mismatch between an in-phase (I) signal and a quadrature-phase (Q) signal and a communication system including the same.
In wireless communication systems, radio frequency (RF) transmitters usually transmit data over two channels, i.e., an I channel and a Q channel. Accordingly, an I local oscillation signal and a Q local oscillation signal which have a 90-degree phase difference therebetween are required to perfectly restore a signal. When the phase difference between the I local oscillation signal and the Q local oscillation signal is not exactly 90 degrees, a bit error rate increases in a finally restored signal. In particular, when a direct conversion receiver or an image-reject receiver, in which a signal is divided into two channels at high frequency, is used, a mismatch between an I signal and a Q signal may cause serious problems in an overall system.
In actual RF receivers, the characteristics of delay cells included in a local oscillator do not ideally coincide with each other due to a difference in the thickness of an insulator, the size of an element, or the space between elements, various crystal structures of semiconductor materials, or layout mismatch. Such disagreement between the characteristics of the delay cells causes a phase mismatch between an I local oscillation signal and a Q local oscillation signal output from the local oscillator, which is a major cause of I/Q mismatch in a receiver. Furthermore, a mismatch between elements on I and Q paths of the receiver also causes the I/Q mismatch in the receiver.
To overcome this problem, a method of compensating a baseband I signal and a baseband Q signal which have passed through a mixer and a method of compensating an I path and a Q path of an RF signal have been introduced. As for these methods, however, a phase shift block for compensating for the phase mismatch between an I signal and a Q signal is additionally required and since an inherent amplitude mismatch needs to be considered, a phase mismatch compensation range is limited.